This thesis re-evaluates the early nineteenth-century treatment of insanity and evaluates, for the first time, the work amongst the insane of Matthew Allen MD. It is written in the form of a biography, the primary source of which is the unpublished manuscript Memoirs of Oswald Allen held in the York Reference Library. Other relevant documents and letters have been found in the Essex County Record Office and in archives in Lincoln, Northampton, Dundee, York and Holborn. A variety of literary sources in libraries across the country and books which Allen wrote have been used. The thesis is eight chapters in length and divided into four chronological parts. It contributes to the history of psychiatry at an important, but often neglected, period and provides details of a man whose name has been previously known only because of his connection with major literary figures. For the first time information is brought together to reveal his contribution to the treatment of the insane and his involvement with other aspects of culture. He is revealed as a pioneer rather than a genius. He sought for causes of insanity and effective counteractions and showed his increasing belief in psychological over physical causes. He maintained faith in the efficacy of Moral Treatment even when under pressure from his colleagues to focus on other stratagems. Allen's childhood and youth were affected by an obscure religious sect. His personality was deeply flawed. He was gaoled twice and suffered two bankruptcies. He nearly cured one poet while bringing another to the verge of mental collapse. His personal struggles aided his understanding of insanity but finally led to his own professional downfall. The conclusion is that the principles for which he stood in treating the insane were early, but genuine, precursors to modern psychiatric practice, often obscured by later nineteenth-century attitudes and treatments.